Draft tube



May 7, 1929.

J. D. 4scovlLLE DRAFT TUBE Filed Oct. 4, 1927y 2 Shewts-Sheel atroz mud May 7, 1929- J. D. scovlLLE 1,711,907

' DRAFT TUBE Fild 0pt- 4, 1927 2 sheets-sheet 2 nventoz Patented May 7, 1929.

UNITED smilies PATENToFFlcE.

JAMES D. SCOVILL, OF YORK, PENNSYLVANIA, ASSIGNOR TO SQMORGAN SMITH COMPANY, INC., 0F YORK, PENNSYLVANIA, 'A CORPORATION OF PENNSYLVANIA.

DRAFT TUBE.

This invention relates to draft tubes, and

particularly to the elbowv type formed of concreteor other analogous material, or in some instances formed of metal. The 'pres ent invention embodies an improvement of the structure disclosed by the pending application of George A. Jessop, improvements in draf-t tubes, filed March ll, 1925, Serial No. 14,850. 'The same structural advantages in draft tube structure 'are sought andv desired to be maintained in the present struc ture as in the original improv-ed elbow draft tube disclosed by the aforesaid application, the material variation in the structure of the outlet leg ofthe tube and a moreeflicient result in operation being the distinguishing features of the present improvement. It has been discovered that there is a higher velocity at the bottom and outside edgesv of the tubev than at the top centerfrom points starting well into the downstream curvature of the elbow and continuing to the outlet of the tube. This variation in velocity begins shortly after the tube starts to bend, and becomes a maximum at or near the end of the elbow and decreases towards the outlet. In order to obtain the best possible efficiency in a draft tube of the elbow, or any other type, it has been found necessary to so form the tube that the water remains infull flowin'g contact with all surfaces of the tube, which is accomplished to a very material extent by a novel curvature of the elbow in this class of elbow draft tubes, as speciied in the aforesaid application. In accordance with the features of this improvement a more eflicient and complete or full flowing Contact with the surface of the outlet leg of the tube is obtained by lling in the top of the tube at the center along the horizontal leg and for a distance upwardly into the downstream portion of the elbow top curve, and thereby overcome the formation in the tube of a comparatively dead space at the center and top of the horizontal leg or outlet portion of 'the tube, and thereby. secure a more even distribution of water in all parts of the tube. As the water flows downwardly through the tube from the entrance and is gradually turned from a vertical direction by the upstream curvature of the elbow, there is a natural spreading effect which increases and becomes more noticeable at what Application, med 'october 4, 1927. semi No( 224,016.

stream curvature of the elbow Vsection the spreading` effect yis slight and becomes greater in the successive portions or lsections thereof until its reaches its maximum at or near the final section and where the elbow merges into the outlet or horizontal leg of the draft tube. The velocities in these tubes, particularly when used for turbines under very large heads, are quite high, andthe spreading action is' therefore quite rapid and causes a large portion of the water-to pass to the Voutside curved periphery of the tube at the final sections of the elbow or near the terminal 'of the latter situated adjacent to the horizontal leg of the tube outlet. The water at the outside of the tube is therefore assuming a spiral motion but flows forwardly along the tube at a more rapid rate than its rate of spiral revolution, the spiral movement ofthe water being insufficient t'o force or throw the water to the center of the tube and permitting a void to bev formed at the center of the tube, which should be filled or rectified by Vchange of" shape of the tube to eliminate eddies and partial voids.

The general operation of the present tube within the length of the curvature complete is the same as that disclosed in the pending application above noted, but in the present structure there is a modification of structure to attain a more satisfactory and complete operation and thereby overcomethe slight disadvantages present in the prior structure The improvement set forth herein is particularly advantageous where it is desirable to install elbow draft tubes of comparatively small vertical height and short horizontal length. rlhe improved elbow has the same curvature on the upstream surface and the same shape at the bottom vof the horizontal leg, and it has the same construction and easement curves on the downstream, or .upper, side ofthe elbow bend, throughout the bendy at the outsideportions. ie center portion of the upper side of the elbow bend, near theV end of this part of the tube, is modified by filling in, or reducing the area by means of a flat top of novel form, with, preferably, approximately straight sides. It is not intended that the improved draft tube be limited to any particular rate of increase of area or to any particular rate of decrease of velocity. Further, in the present improved structure, wherever it is possible, this flat roof portion embodies a straight line construction and the curved, or circular, sides of the prior structijlre are replaced with vertical sides, sometimes straight fillets at the farthest possible upstream section of the tube consistent with satisfactory results. This simplifies and cheapens the work required to construct the tubes, whether made of concrete, metal or other material.

l The object of the present invention therefore is the provision of a flat top portion for the horizontal leg or outlet of the draft tube in contradistinction to a top curved contour to obtain a more uniform velocity at the outlet together with a novel arrangement of piers within the horizontal outlet to secure a more uniform flow of water through the horizontal leg with the greatest possible reduction of "velocity from the entrance of the outlet of the tube, and wherebyV the formation of a dead space at the center and upper portion of the horizontal leg is entirely avoided and a more even distribution of the water over the remaining passages is obtained, thus overcoming the disadvantage of having the water break away in the top or downstream curve of the elbow.

The present invention consists essentially in the preferred construction and arrangement of parts which will be more fully hereinafter described and claimed.

The accompanying drawings illustrate the improved draft tube yformed of concrete or analogous cementitious material, but it will be understood that the same essential features of invention may be included in a metal or sheet steel draft tube.

In the drawings:-

Fig. 1 is a longitudinal vertical section through an elbow draft tube embodying the improved features of the invention.

Fig. 1a represents a section taken horizontally through the upper end of the draft tube shown in Fig. 1, the top flange being omitted.

Fig. 2 is a horizontal section on 2. 2. Fig. 1.

Fig. B is a horizontal section on 3. Fig. l.

F l is a horizontal section on l. 4l. Fig. 1.

o is a transverse section on 5. 5. Fig. 1.

C. is a transverse section on 6. 6. Fig. 1.

Fig. 7 is a transverse vertical section on the line 7. 7. Fig. 1.

Fig. 8 is an end elevation of the outlet terminal or horizontal leg of the tube.

Fig. 9 is a horizontal section taken through the line the line 'he line the line the line the center of a part of the tube, and particularly through the outlet or horizontal leg and containing rearwardly a distance through the elbow bend, the upper inlet of the elbow being shown in dotted lines.

The numeral 5 designates a concrete or other cementitious structure in which the improved tube is suitably formed, the latter comprising an upper inlet extremity 6 over which the runner or wheel is adapted to be mounted inthe usual manner. The concrete or other analogous structure 5 may be continued upwardly any suitable distance to serve as a base support for the installation. of the remaining part of a turbine or other water power organization, and also for the purpose of supporting a power house in which the turbine unit or units are disposed. The upper member 7 of the improved draft tube is shown as composed of sheet metal down to the point 8, the remaining part of the draft tube being shaped in the concrete or other material. lt will be understood that the upper member 7 of the draft tube, which may be specified as the inlet member may in some instances be constructed or shaped in the concrete. This upper inlet member 7 to a point a short distance below the plane of section 2. 2. is concentric with relation to the axial line 9a which is also the vertical axis of the runner or wheel and the turbine shaft. rlhe upper inlet member 7 may be slightly bowled and regularly flares in a downward direction as shown, or it may have a straight taper or Hare. At a comparatively short distance below the plane or section on the line 2. 2. and as indicated by the plane of section 3. 3. F ig. 3, the draft tube begins to assume an elliptical contour, and this configuration increases gradually in the present instance through to the plane of the section 6. G., as indicated by Figs. 3 to 6 inclusive. In order to arrive at this construction, the curve 11 of the upstream or lower side of the elbow `begins prior to the curve 12 of Athe downstream or forward upper wall f the draft tube elbow. rlhe rear or upstream curve 11 comes from the vertical to the horizontal in an arc with a practically constant radius, or in other words, with ay constant curvature. The cirvature of the downstream or uppr face of the elbow starts at a materially lower elevation than Jthe upstream curve 11 when considering a vertical tube construction only. ln other words, the curvature 12 of the downstream face of the lbow iirthe downstream direction starts much later than the curvature 11 of the up'- stream face. rlChis downstream curve 12 of the upstream face is an easement curve, that is, at the beginning thereof there is a long radius of curvature and this radius is gradually decreased and becomes aminimuin at or near the end of the curve as at 9 for lOO the outside portion of the tube, and as at 13 for the central portion of the tube. In a vertical setting the points are about at the horizontal. Frein the point of the plane of the section 7. 7. to the point 18 or end' of the easement curve there is a modification of structure in the present improved invention relatively to that disclosed in the prior application heretofore noted for the purpose of assisting the water to remain in .a more perfect full fiowingcontactwith the downstream or upper portion of the elbow of the draft tube, and assist in maintaining a practically equal velocity'of water at a given section of the draft tube. The maintenance of an equal vvelocity at all points in a given section of a draft tube, said section being taken approximately at right angles to the longitudinal center' line, is necessary in order to maintain smooth flow and high efficiency in the tube. Again, for the purpose of illustration, let it be assumed that the tube is divided into three distinct parts. rlvhe first part is the vertical section or inlet member 7 with a straight vertical center line immediately below the runner. -The sections at this inlet part or member of the tube .are true, or approximately .trueeircles, and for convenience of description the words breadth and width will be applied to different sections of the tube, the breadthl being intended to mean the distance between the walls of the 4tube as cut by a plane passing through a longitudinal center` line thereof, and by i width is meant the distances between the wall of the tube as measuredatright angles to the foregoing plane, each measurement passing through the longitudinal center line of the tube.

. The second part of the tube is the curve or elbow section 10. The breadth of they tube is a maximum at approximatelyV the end Vof the rst part andy ,at approximatelyv the beginning of the second part or section or `elbow 10. The breadth of the second part or elbow member 10 relatively decreases from its maximum at they 'entrance of this second part or section to its minimum at or near the end of the elbow, as at 9 and 13. In other words, the upstream or lower face of the draft tube defined by the curve 11 approaches and ,gets nearer to the downstream or upper face of the draft tube define-d by the Vcurve 1Q. f At the same time the width or lateral extent of the draft tube is increased all along the bend or elbow section 10, and this increase is such that the area of the tube is constantly increasing, so that the velocity of the water in the tube is constantly decreasing, or the velocity head is constantly being converted into pressure head. The reduction in the breadth ofthe tube from the beginning of .the upper end of the second section or part or elbow 10 is accomplished by making a curvature .of thev upstream and downstream faces ofthe tube, or the lower and upper sides of the tube, in thecurvature heretofore'lspecified, and further because the curvature of the downstream or upper face or side isstartedat a considerably lower point d even be decreased, provided the width or lateral extent of thetube be increased a sufficient degree to maintain the continuously increasing area as the water approaches nearer and nearer the outlet end 16. As hereinbefore indicated, from the entrance of the improved tube to t'he outlet end thereof the area is continuously increasing and .therefore the velocity of thewater is continuously decreasing.

The present improvement, in view of the l structure heretofore disclosed andthe eopending vstructure disclosed by 'application Serial No. 199,530, filed June 17, 1.927 in the name of George A. Jessop, preserves in the main the same structural conditions as just enumerated with structural modifications or changesv in the upper part of the outlet leg or sectionl 15, and continues inv the same plane into the downstream .part of the elbow as far'upwardly as about the plane of the section indicated b the line 4. 4. shown by Figure k1, and which consists in directing supporting piers 19 and 20, as clearly shown 1 by Figure 9, and are located on opposite sides of the longitudinal center `of the outlet end 16 of the leg. As indica-ted by the cross sections, in Figures 6 and 7 the fiat top assumes an upward trend or inclination fully from the outer portion of the elbow to lthe end 16 of the ieg 15, and extending partially inwardly land upwardly to the top or downstream curve of the elbow or as near as farback inwardly and upwardly as approximately the plane of the section 5. 5. The opposite sides of the elbow as shown by Figures '3 and 4 are curved as at 21, but this ciurvature gradually merges or is changed into nearly straight or vertical side structures as at 22, Figures 5, 6, 7 and 8, and the angular corners formed by the intersections of the outlet extremity of the sides of the point of change te the vertical structure being filled at top and bottom by fillets 23, as shown by Figures 5 and. 6 for a portion of the length of the leg 15, or, to compensate for a change of the configuration until there is a full side mergence into full vertical structures, shown by F i gures 7 and 8. l--lence the outlet leg l5 of this further improved, form of draft tube as compared to the structure disclosed by application Serial No. 14,850 heretofore referred to, is filled at points which aid in overcoming the tendency of the water to break away from the top or downstream curve of the elbow at the plane of the sections t and 5 for instance, and eliminating from the tube the emparaf tively dead spa-ee at the center of the top of the horizontal leg l5 and obtaining a more even distribution of the water over the remaining passages and also avoiding a tendency to spiral motion of the water along the side portions of the leg, the latter having at the top a substantially straight line construction. rlie piers 19 and 20 are positioned with the upstream ends thereof close to the side walls of the tube. As indicated, ythe velocity at the side walls is somewhat higherthan at the center, and therefore, ther greatest quantity,T of water passes out of the tube along the sides. These piers collect some of this water from the sides and distribute it smoothly and einiciently to the center of the tube. The piers are sloped or converged away from the outside of the tube and toward each other. The slope or convergen-ce must be such that the outside sections of the tube forinedbetween the piers and the side walls will maintain the water in full flowing Contact with all surfaces of this partof the tube, the piers approaching each other in the center. The water in this part of the tube will, of course, remain in full flowing contact with all surfaces. By these piers as shown, the velocity at the center of the draft tube can be made approximately equal to that outside, thus securing uniform velocity and materially increasingfthe efficiency of the draft tube.

Furthermore, these piers 19 and 20 will also serve as supports for a power house structure and also strengthen the out-let leg.'

This improved structure of elbow draft tube produces full flowing water Contact with all sides throughout the lengt-h of the tube, and the water is graduallyl decelerated towards the outlet end 16 of the tube and is finally discharged into the tailrace.

lVhat is claimed as new is:-

l. A draft tube having an inlet extremity concentric with relation to a central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by an upstream, practically constant radius curve and a downstream easement curve, the draft tube being increased in width and terminating in an outlet extremity having means therein for equalizing the velocity of the water flow downstream throughout the width thereof.

2. A draft tube having an inlet extremity concentric to a central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by means of an upstream, practically constant radius curve and a downstream easement curve and proportionately laterally increased in width and v terminating in an outlet leg, the said outlet leg having a flattened form and having means therein for increasing the velocity of the water fiowing through its central portion relatively to that of the water flowing along its sides, the draft tube from its inlet to its outlet extremity increasing in area as a whole. i

3. A draft tube comprising an inlet meme ber and an outlet leg with an elbow therebetween, the said elbow being decreased Vin breadth from the upstream towards the downstream portion thereof by means of an upstream, Lractically constant radius curve and a downstream easement curve, said easement curve starting at a materially lower elevation than said consta-nt radius curve,

and the said elbow bend being correspond-v ingly and proportionately increased in width, the out-let leg having a flattened form and having means therein for reducing the vvelocity of the water flowing along its sides tinuing with this lateral increase through out the elbow in a direction from the upstream to the downstream portion of said elbow bend, the elbow bend having an upstream, practically coiisiant radius curve and i downstream easement curve, the outlet extremity having a trans 7ersely straight flaitened top portion with piers therein on opposite sides of the center converging towards the end of the outlet extremity. Y

5. A draft tube having inlet and outlet extremities with an elbow bend therebetween, the inletextremity being circular and the tube as an entirety from its inlet extremity being increased in lateral extent and continuing with this lateral increase through the elbow in a direction from the upstream towards the downstream portion of said ben-d, the elbow bend having an upstream,- practically constant .radius curve a down` stream easement curve, the outlet extremity having a transversely flattened formfand having means therein for rela-tively reducing the velocity of the water flowingalong its sides and forrelatively increasing thevelocity of the water" flowing at the intermediate portion of its width.

v6. A draft tube having inlet.y and outlet extremities with an elbow bend therebetween and gradually increased in lateral extent from thel inlet extremity which is circular in contour to the outlet leg at a distance beyond the termination of the elbow bend, the elbow bend correspondingly and gradually increasing in lateral extent throughout the formation 'thereof towards the outlet extremity, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve, the elbow also gradually decreasing in vertical extent towards the outlet extremity, and the outlet extremity having a flattened form and having piers arranged angularly therein to increase the velocity of the water flowing intermediately of its width relatively to that of the water fiowing at its sides.

7. A draft tube having inlet and outlet extremities with an elbow bend interposed between said extremities and continuous therewith, the said elbow being materially flattened in a transverse vertical direction within the area of the bend portion thereof and also increasing in width within the area of the bend and regularly continuing into the out-let extremity, the elbow bend having an upstream, practically constant radius curve and a downstream flattened contour which is transversely straight and having an voutlet leg and piers therein arranged angularly with respect to its sides to reduce the velocity of the water flowing at the sides of the leg relatively to that of the water fiowing through the portion thereof intermediately` of its width.

8. A draft tube having inlet and outlet extremities and an elbow bend between the two extremities, the inlet extremity beingv concentric with relation to a central axis and regularly continuing into the elbow bend, the* elbow bend regularly decreasing in breadth by an upstream constant radius curve and a downstream easement curve differing from the upstream curve, the said bend also positively increasing in width diver-gently, and said divergence regularly and fullv continuing into the outlet extremity of the dtube, the dutlet extremity of the `tube having a transversely straight flattened top and straight side portions, the said flattened top portion of the outlet extremity extending a distance rearwardly into the elbow bend, and the opposite curved sides of the bend merging into vertical sides of the said outlet extremity, the saidy outlet extremity also having a pair of piers' disposed on opposite sides of the center thereof andconverging towards the outer endet the sai-d outlet extrem'ity.

9. A draft' tube having inlet and outlet portion having an easement curve which is formed in the centerwith a dip towards and merging into the top of the outlet extremity and providingl an easement curve with less y'apid change of curva-ture at its terminal and which merges into the outlet extremity which has a. transversely fiattened form having water directing members which extend longitudinally therein, said members converging towards one another and diverging from the adjacent sides of the flattened outlet in a direction towards the end of the outlet extremity.

l0. A draft tube having inlet and outlet extremities with an elbow therebetween, the elbow being contracted in breadth and expanded in width and the outlet extremity having a transversely fiattened portion and means in said outlet extremity for increasing the velocity of the water liowing in the center relatively to that of the water flowing at the sides thereof. i

l1. .An elbow draft tube having an inlet extremity concentric with relation to a central axis and wherein also the elbow bend is contracted in breadth and expanded in width and continued into an outlet leg with an upwardly flaring top portion, said outlet leg being transversely flattened and having therein means to increase the velocity ofthe water flowing in its center and to relatively decrease they velocity of the water flowing along its sides.

l2. A draft tubevhaving a circular inlet, an elbow bend contracted in breadth and expanded in width and continuous with said inlet and operating to cause a round column of water entering the draft tube ahead of the elbow bend to be vflattened in breadth and expanded in width, and an outlet extremity having a flattened top which is transversely straightand upwardly fiares from the said elbow bend and is provided with a pair of 'piers on opposite sides of the center which converge relatively to one another in a direction towards the end of the outlet extremity to eliminate eddies and voids.

13. A draft tube having an intermediate elbow bend flattened in breadth and expanded in width and an outlet extremity with a transversely straight flattened top portion extending from the elbow bend to the end'of the outlet extremity and also provided with a pair of piers in the outlet extremity and portions with an elbow therebetween, the

elbow being contracted in breadth and eX- panded in width in a direction from its inlet towards its outlet, and the outlet portion having an outlet passage which is between and separated from its sides and decreases in area in a downstream direction.

15. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and eX- panded in width in a direction from its inlet towards its outlet and the outlet portion having water outlet passages at its sides which increase in area in a downstream direction and having an intermediate water outlet passage which decreases in area in a Y JAMES D. scoviLLn 

